I can see both sides of this.., the HV who doesn't know your wife so doesn't know how to judge the situation and yours and your wife's feelings about what is going on.
Its not easy but I'm afraid she is going to have to see someone. Midwives are only supposed to be the main point of contact for the first two weeks after a baby's birth. Is there someone your wife can substitute for the HV.., like a GP she trusts? Altho I am afraid this may not stop the HV from feeling like she must be involved, but it may help.
However, I am afraid I can see problems ahead as has been mentioned. Your wife is going to have to deal with a lot of people because of your child.., like school teachers etc and not taking your child to parent child groups/nursery etc will mean your child won't have opportunities that help a child develop. Your child may also pick up on your wife's nervousness and enact that him/herself I'm afraid, which can't be good. Please try and understand the ramifications of this. Its not judgement, its not simply trying to force u both to do something u don't want to do., there are reasons for people trying to persuade you to do these things.
If she has tried various therapeutic approaches and is still suffering fairly inhibiting anxieties.., they haven't been as helpful as they could have been and maybe she needs to try something else., or a different approach. I looked up 'anxiety websites' on the web and found several references. Could one of these advise on things that might help her.., perhaps they could offer her support that might possibly help her confidence?